Journalist Martin Dillon last week published a new book, The Sorrow and the Loss: The Tragic Shadow Cast by the Troubles on the Lives of Women, which includes a number of claims about the circumstances of the 1987 bombing.

In a statement, Belfast-based KRW LAW said the families it represents are “deeply concerned” about some of the contents of the book, which they say raise “issues of grave concern”.

The claims — some of which Mr Dillon says should be treated with caution — include that MI5 tampered with the timer on the Provisional IRA bomb in order to undermine the paramilitary group’s popular support, and that state assets were involved.

The book also alleges that the UK and Irish governments have access to materials about the bombing which they have failed to publish.

KRW LAW said: “These allegations are against the British and Irish governments and their respective intelligence agencies.

“Post the Legacy Act, the only available mechanism to investigate these highly sensitive allegations is by way of a public inquiry under section 1 of the Public Inquiry Act (NI) 2005.

“We are now writing to the Secretary of State, the Home Office and the Irish government urging a s.1 public inquiry analogous to the Omagh bomb inquiry.”